Those armatars users have that cannot be selected are any of the following:
1) Seasonal armatars from past contests. 2) Armatars that had a high AP requirement in AG2 (the previous AG). 3) Armatars that require a special status (knight, mod, admin, or developer), including custom armatars.
As for custom armatars, there is no way to create them outside of armatar contests, which are found in this forum.
Exactly what @Patrick2011 said @DarthTyrannausarus... enter an official Armor Games' Armatar Contest to submit your own created artwork for an Armatar, but... beware of plagiarism! It must be made by yourself completely and fitting the current theme from the contest. Try it! =)
